A method for manufacturing a laminated body has heretofore been known, in which a transparent conductive layer peelably laminated on a temporary supporting body is transferred to a transparent substrate composed of plastic material through an adhesive agent, thereby producing a laminated body including the transparent substrate and the transparent conductive layer. Such a transparent conductive layer is typically composed of an indium tin oxide (ITO).
For example, Japanese Patent Application Laid-Open No. S60-231396 discloses a transfer type laminated body in which an ITO layer is peelably formed on a temporary supporting body. This Laid-Open further discloses a method in which an ITO layer is vapor-deposited on a supporting body composed of a Teflon film, thereafter, the vapor-deposited ITO layer is subjected to heat treatment in an oven at a temperature of 300xc2x0 C. to decrease the electrical resistance of the ITO layer, and the ITO layer of the transfer type laminated body is transferred to a polymethyl-methacrylate substrate. It also teaches that an aromatic polyimide can be used as the supporting body. Moreover, Japanese Patent Application Laid-Open No. S59-204542 discloses a method in which an ITO layer is vapor-deposited to a heat-resisting substrate which has been subjected to peel-off treatment and thereafter, the ITO layer is transferred to a film through an epoxy resin adhesive agent having a low temperature hardening property.
Japanese Patent Application Laid-Open No. S58-177345 discloses a method in which an ITO layer is sputtered to a mold release treatment surface of a polyester film, and the ITO layer is thermally press-bonded to a polyvinyl butyral sheet so that the ITO layer is transferred to the surface of the polyvinyl butyral sheet.
Japanese Patent Application Laid-Open No. S59-151705 discloses a method in which an ITO vapor-deposited film layer is formed on a temporary carrier such as a Teflon film and a polyimide film and then the ITO layer is transferred to a surface of a plastic transparent substrate through an adhesive agent having a thermo- or photo-hardening property.
Moreover, Japanese Patent Application Laid-Open No. H07-80980 discloses a transparent conductive transfer sheet in which an ITO layer and an adhesive layer are sequentially laminated on a substrate composed of a film having a low surface energy. It also teaches a stretched polypropylene as a specific example of a film having a low surface energy.
On the other hand, Japanese Patent Application Laid-Open No. H02-174011 discloses a method in which a resin coating film is laminated on a temporary supporting body (release sheet), an ITO layer is laminated on the resin coating film and a thermally adherable adhesive agent is laminated on the ITO layer to thereby form a transfer sheet, and the transfer sheet is press bonded to a glass substrate while heating, so that a laminated body composed of the ITO layer and the resin coating film is transferred thereto through the adhesive layer. This Patent Application Laid-Open teaches that a synthetic resin film such as polyethylene, polypropylene, polyester and the like can be used as the supporting body and the a mold releasing treatment is executed, where necessary, with respect to the supporting body. It is also disclosed that a peelable layer functions as a protective film of the ITO layer that as a suitable material thereof, one can be selected from the group consisting of celullosic resins, acrylic resins and nylon resins and that the thickness of the peelable layer is 1.5 xcexcm or less and preferably 1 xcexcm or less.
Furthermore, Japanese Patent Application Laid-Open No. H11-24081 discloses a method in which a laminated body including polyimide resin layer and an ITO layer laminated on a temporary carrier by vapor-deposition, sputtering, pasting or the like is peeled off from the polyimide resin layer and transferred. It also teaches that a film having a heat-resisting property such as kapton, polyetherimide, etc. is used as a supporting body. At that time, the polyimide resin layer is also transferred from the temporary carrier to the transparent substrate and this polyimide resin layer is formed to have a thickness of 100 nm suited to be used as an orientation film.
In the above-mentioned conventional methods, an ITO layer is formed on a heat-resisting plastic film and then transferred to a plastic film or glass substrate through an adhesive agent. Accordingly, no consideration is paid to the variation (expansion and contraction) of the film occurrable at the time of formation of the ITO layer on the plastic film.
Moreover, this adverse effect becomes more manifest as the pattern precision of the ITO layer becomes finer. However, the conventional methods pay no attention to this fact.
For example, in the series of a transfer laminated body and a transfer method discussed in the former method, the ITO layer is laminated directly to the temporary supporting body and no resin layer is disposed together with the ITO layer between the supporting body and the ITO layer. In a constitution like this, it is practically impossible to etch the ITO layer on the supporting body so as to form a pattern. The reason is that since the adhesion between the ITO layer and the underground layer is not good, an etching liquid is liable to permeate into an interface between those layers at the time of an etching treatment to the ITO layer and as a result, the patterned ITO layer is peeled off.
In the latter method, the ITO layer is formed on the plastic film as a supporting body. Accordingly, when the ITO layer is shaped into the form of a pattern in that state, the plastic film is expanded and contracted by thermal expansion and/or temperature at the time of formation of the pattern. This makes it impossible to form an ITO layer with a high degree of precision.
Moreover, since a plastic film is used as the supporting body, another problem is encountered in which a long dimensional accuracy cannot be obtained due to distortion of the film. Particularly, in the case where a color filter is formed on the ITO layer, it is necessary to make a positional alignment between the ITO layer and the color pixels constituting the color filter or between the color pixels. However, if the pattern precision (positional precision) is not good, there is such a vital shortcoming in that the color pixels cannot be provided on the ITO layer correctly.
For example, the thermal expansion coefficient of polyimide (Kapton) as a representative heat-resisting high polymer is about 4xc3x9710xe2x88x925/xc2x0 C. This means that if the temperature is changed 1xc2x0 C., a film (polyimide) having a length of 30 cm is expanded by 12 xcexcm.
However, it is difficult to control the temperature within a range of 1xc2x0 C., in the actual manufacturing process. Also, if it is taken into consideration the fact that a space width of the adjacent lines of ITO for a crystal device is normally 10 to 20 xcexcm, there can be encountered with such inconveniences that due to variation of the heat processing temperature at the time of manufacture, a color pixel of the color filter layer is overlapped with a different color pixel or placed astride over different color pixels.
As an example of the change in length dimension due to variation of temperature, one test example is taken up here, in which a film composed of a polyether sulfone resin was used. Only by dipping this film in water for cleaning, the length of 30 cm was elongated 150 xcexcm. This film was treated at 100xc2x0 C. for drying and the temperature was then returned to a normal temperature. As a result, the film was contracted by 300 xcexcm compared with the length before washing. This film was stored at a constant temperature and humidity, three days were required until the length gets stabilized. If the length dimension of the film is so extensively changed as just discussed, a difficulty is accompanied with not only the positional alignment at the time of manufacture of the ITO and color filter layers but also the positional alignment between the ITO and a driver circuit.
It is, therefore, an object of the present invention to provide a transfer body and various methods such as a method for reproducing the transfer body, a method for forming a transparent conductive layer using the transfer body, and the like, which is capable of solving the above-mentioned problems.
According to a first aspect of the present invention, there is provided a transfer body including at least a peelable layer, a transparent conductive layer and an adhesive layer all sequentially laminated on a heat-resisting and rigid supporting body, wherein the peelable layer is formed to have a pull strength of 100 g/cm or more. The heat-resisting property possessed by the supporting body must be large enough to withstand the heat treatment to the various layers on the supporting body and the rigidity possessed by the supporting body must be larger than that of the opponent member to which the layers on the supporting body are to be transferred.
According to a second aspect of the present invention, there is provided a method for reproducing a transfer body, the method comprising, at the time of reproducing a color filter layer formed on a transfer body, the steps of removing a color filter layer from a supporting body by a plasma etching method in which oxygen is chiefly used or by a reactive ion etching method (RIE) and then sequentially forming at least a color filter layer and an adhesive layer on the supporting body.
According to a third aspect of the present invention, there is provided a method for forming a transparent conductive layer using a transfer body comprising the steps of forming a transfer body by sequentially laminating at least a peelable layer, a transparent conductive layer and an adhesive layer on a heat-resisting and rigid supporting body, adhesively sticking the transfer body to one surface of a film composed of plastic material through the adhesive layer, and peeling off the transfer body inclusive the peelable layer from the supporting body through the peelable layer, thereby transferring the transparent conductive layer to the film composed of plastic material, wherein the peelable layer has a pull strength of 100 g/cm or more.
According to a fourth aspect of the present invention, there is provided a method for forming a transparent conductive layer using a transfer body comprising the steps of forming a transfer body by sequentially laminating at least a peelable layer, a transparent conductive layer and an adhesive layer on a heat-resisting and rigid supporting body, adhesively sticking the transfer body to one surface of a film composed of plastic material through the adhesive layer, and peeling off the transfer body inclusive the peelable layer from the supporting body through the peelable layer, thereby transferring the transparent conductive layer to the film composed of plastic material, wherein one end portion of the film composed of plastic material is temporality fixed to a roll having a diameter of 50 mm or more and preferably 100 mm or more and thereafter the roll is substantially rollingly moved to peel off the transfer body inclusive the peelable layer from the supporting body through the peelable layer, thereby transferring the transparent conductive layer to the one surface of the film composed of plastic material.
The supporting body used in the present invention for supporting the transfer body has a heat resisting property having a thermal expansion coefficient of 1.5xc3x9710xe2x88x925/xc2x0 C. or less and has a rigidity not readily changed in dimension due to change of temperature. A suitable supporting body includes a blue plate glass (thermal expansion coefficient: 9 to 10xc3x9710xe2x88x926/xc2x0 C.). In the case where the transparent conductive layer and the color pixel pattern are fine pitched thereby making it difficult to align the transparent conductive layer with the color filter composed of such color pixels as Y, M, C or R, G, B, a low thermal expansion glass (4 to 5xc3x9710xe2x88x926/xc2x0 C.) is preferably used.
The peelable layer used in the present invention is a resin material having a high heat-resisting property such as a polyimide resin. The peelable layer is required to have an adhesion of about several g/cm to 100 g/cm under the condition of 90 degrees peel-off between the peelable layer and the supporting body.
Although it is preferred that the adhesion is smaller from the view point of peeling off the transfer body from the supporting body so as to be transferred to the film, it is necessary for the peelable layer to have more than a certain degree of adhesion so that it can withstand such manufacturing processes as washing and etching which are required for shaping the transparent conductive layer into the form of a pattern. Moreover, the peelable layer is required to have a pull strength of 100 g/cm or more (per width of 1 cm). The reason will be described later.
The pull strength of the peelable layer can be increased by enlarging its thickness. It is also required for the peelable layer to have resisting properties to temperature at the time of forming the transparent conductive layer and to chemical(s) used at the time of patterning the transparent conductive layer. In addition, it is, of course, required for the peelable layer to have a favorable adhesion to the transparent conductive layer.
As the material of the peelable layer, polyimide is the best. By applying the polyimide to the supporting body so as to form a thickness of 1.3 xcexcm or more and preferably 2 xcexcm or more, the required pull strength can be obtained.
As the transparent conductive layer of the present invention, indium tin oxide (ITO), indium oxide, tin oxide or the like can be used. Among them, ITO is currently considered as a material capable of exhibiting the best physical properties.
When ITO is formed into a layer by such layer forming means such as sputtering, ion plating or the like and under the temperature condition of 150xc2x0 C. or higher, there can be obtained a layer having a low electrical resisting property. Although a layer having a low electrical resisting property is difficult to obtain, ITO can also be formed into a layer by the sol-gel method. By patterning such obtained transparent conductive layer, a transparent electrode is formed. This patterning can be performed by the known process of photolithography. In the case the adhesion between the peelable layer and the supporting body is several g/cm or less by 90xc2x0 peel test, the peelable layer is peeled off during the patterning process of the transparent conductive layer. Since a supporting body having a small expansion coefficient is used at that time, a patterning with an excellent dimensional precision can be obtained.
By disposing a barrier layer of an inorganic material composed of SiOx, SiN, Al2O3, or TiO2 between the peelable layer and the transparent conductive layer, there can be provided the function for protecting the transparent conductive layer and for serving as a gas barrier after the transfer body is transferred to the film.
The inorganic barrier layer can be formed in such a manner as to have a thickness of 0.1 xcexcm or less by a vacuum layer forming means such as a spattering method, an ion plating method or the like. Thereafter, an intermediate layer and a color filter layer may be formed in accordance with necessity.
As the intermediate layer, an acrylic or alkyd resin or an inorganic material such as SiOx can be used. It is also accepted that an inorganic material such as SiOx serving as the barrier layer also serves as the intermediate layer. Such an intermediate layer as just mentioned serves to ease the stress, particularly the stress caused by hardening contraction of the adhesive agent at the time of transfer by sandwiching the transparent conductive layer between the peelable layer and the intermediate layer, so that an occurrence of cracks to the transparent conductive layer is prevented. Furthermore, the intermediate layer serves to protect a color filter layer, where there is a provision of such a color filter, at the time of peeling off the peelable layer.
The color filter layer can be formed by a general method using a photolithography. At that time, since the color filter layer is formed on the supporting body of the type as mentioned above, no problem occurs to the positional alignment. Moreover, since the process for forming the color filter layer includes a wet process as in the process for forming the ITO, it is desirable to use a supporting member which is hardly varied in dimension which would otherwise be varied by temperature and humidity.
The transparent conductive layer and the color filter layer thus formed on the supporting body are transferred to a film composed of a plastic material. As the plastic material, polyether-sulfone, polycarbonate, or the like can be used. The film thickness of such a plastic material is 50 xcexcm to 300 xcexcm and preferably 100 xcexcm to 200 xcexcm.
The supporting body with such a transparent conductive layer as ITO formed thereon is stuck to the film composed of a plastic material through the adhesive layer and the adhesive layer is hardened. As the adhesive layer, a layer which is hardened at a normal temperature is preferable for the purpose of maintaining a dimensional precision and a photo-hardening type adhesive layer is particularly preferable.
The adhesive layer used in the present invention must be able to firmly adhere to the uppermost layer such as a color filter layer formed on the supporting body.
There are encountered with some problems when the film composed of a plastic material is peeled off the supporting body through the peelable layer. The problems reside in a fact that at least the peelable layer, the transparent conductive layer and the adhesive layer are transferred from the rigid supporting body to the film composed of a highly flexible plastic material.
That is to say, when the film composed of a plastic material is peeled off the rigid supporting body, the film must be peeled off in such a manner as to be somewhat warped (or bent). At that time, the transparent conductive layer can follow a warping motion to some extent. However, since the transparent conductive layer is an inorganic substance, it is hard and fragile and therefore, cracks are liable to occur when a force is applied thereto in the warping direction. For this reason, it is necessary to control the force applied in the warping direction when the film composed of a plastic material is peeled off the supporting body through the peelable layer.
This problem can be solved by using a roll. By using the roll, the transparent conductive layer is peeled off the supporting body along the circumference of the roll. At that time, the diameter of the roll is set to 50 mm or more and preferably 100 mm or more. By doing so, it can be prevented that an undue warping force is applied to the transparent conductive film so that no cracks occur to the transparent conductive layer.
However, it sometimes happens that when transferring from the rigid supporting body to the film composed of a flexible plastic material, the peelable layer and the transparent conductive layer are partly left remained on the supporting body instead of being totally transferred to the film, depending on the material and thickness of the peelable layer even in the case where a roll having a diameter of 100 mm or more is used for the peeling off operation. At that time, it was observed that the layers to be transferred were peeled off between the transparent conductive layer and the intermediate layer or between the intermediate layer and the adhesive layer which are supposed to have a larger adhesive property than the adhesion between the supporting body and the peelable layer.
Moreover, in the case where a layer composed of an inorganic hard material such as SiOx is formed as an intermediate layer before and after the transparent conductive layer, it was confirmed through an experiment that this phenomenon becomes more manifest.
In this phenomenon, the larger the pattern of the transparent conductive layer is (i.e., the larger the area of the transparent conductive layer is), there is a more possibility for such a layer to be left remained on the supporting body. Even after the transparent conductive layer is transferred to the film, when the layer is subjected to heat treatment or applied with a stress attributable to a high temperature and high humidity test, wrinkles occur in a perpendicular direction to the peeling-off direction. The cause is considered as follows. Since the transparent conductive layer is hard compared with the film composed of a plastic material, the transparent conductive film tends to resist the warping force at the time of peeling-off. Accordingly, in the case where the transparent conductive layer is in the form of a narrow stripe pattern, it is preferred that the roll is arranged in parallel to the mutually parallel patterns and the roll is rollingly moved across the patterns.
In the present invention, when the transfer body inclusive the transparent conductive layer is peeled off the rigid supporting body so as to be transferred to the film composed of a plastic material, the transfer body can be peeled off through the peelable layer (namely, from the interface between the supporting body and the peelable layer). Moreover, as a result of extensive study as to the method for preventing an occurrence of cracks to the transparent conductive layer, it became apparent through experiments that the occurrence of cracks can be prevented by increasing the film strength of the peelable layer.
Inherently, when the transfer body is peeled off the rigid supporting body in order to transfer at least the peelable layer the transparent layer and the adhesive layer to the film composed of a high flexible plastic material, the transfer body is adhesively stuck to the film and so the transfer body inclusive the peelable layer is integral with the film. Therefore, it seems that the transfer body can easily be peeled off through the peelable layer. However, as previously mentioned, by selecting the material of the peelable layer and properly controlling the thickness thereof and by increasing the strength of the peelable layer to the level as mentioned above, the transfer body can be peeled off not only by the adhesive force (adhesion) between the adjacent layers of at least the peelable layer, the transparent layer and the adhesive layer but also the transfer body can be peeled off in such a manner as to raise the transparent conductive layer over the peelable layer. In this way, by using a peelable layer having a predetermined pull strength, the transparent conductive layer can be transferred irrespective of the pattern shape of the transparent conductive layer and the material of the intermediate layer(s). Moreover, the transfer body can be transferred without undue stress applied to the transparent conductive layer. Consequently, wrinkles do not occur to the transparent conductive layer even if it is placed under a stress caused by the heat treatment or high temperature and high humidity test after the transfer body is transferred to the film. Thus, the transferred transparent conductive layer can be enhanced in resistance against heat and resistance against high temperature and high humidity. Although the strength required for the peelable layer affects the adhesion between the supporting body and the peelable layer, the hardness of the transparent conductive layer and the area (shape) of the pattern of the transparent conductive layer, the adhesion between the supporting body and the peelable layer must be restrained in a certain range in consideration of the following process for forming the various layers as previously mentioned. Also, the hardness of the transparent conductive layer must be restrained in a certain range, though there are some differences depending on the method for forming layers, etc. Particularly, in the case where the transparent conductive layer is used as a stripe electrode for LCD, it is important that a transparent conductive layer having a line width of about 100 xcexcm can be transferred. The strength required for the peelable layer at that time is 100 g/cm. In the case of a product including a pattern having a larger line width and a wider area, the strength required for the peelable layer is 150 g/cm.
In the case where the peelable layer is formed to have such a thin layer width as 100 nm as disclosed in Japanese Patent Application Laid-Open No. H11-24081, it is practically impossible to transfer the layer of ITO, etc. formed on the rigid supporting body to a flexible film composed of plastic material or the like. In case of such a thin peelable layer, a peeling interface can be determined solely by how strong or how weak the adhesive force (adhesion) between the layers is. The reason is that since the rigidity of the supporting body and the ITO is stronger than the rigidity of the film and the adhesive agent, the area which is subjected to force at the time of transfer becomes larger than other interface and as a result, the ITO is left remained on the supporting body.
The peelable layer composed of a resin material is left remained on the uppermost layer at the time of transfer of the transparent conductive layer to the film composed of a plastic material. In the case where the transparent conductive layer is used particularly as an electrode for LCD or the like, it is necessary to remove the peelable layer in order to facilitate a smooth driving of the crystal. As a method for removing the peelable layer composed of a polyimide resin, there is a method for removing it using a specific solution such as a mixed solution of hydrazine and ethylene diamine, and an alkaline solution. Since there is a possibility that an adverse effect is prevailed on the adhesive force (adhesion) between the layers due to permeation of the solution from end portions, for example, of the transparent conductive layer, the adhesive layer and the film, it is desirable to remove the peelable layer by suitable method such as a plasma etching method in which oxygen is chiefly used and a reactive ion etching method. However, in the case where the thickness of the peelable layer is increased, the surface smoothness is deteriorated when coated and it becomes extremely difficult to remove the peelable layer. For example, at the time of removing the peelable layer, the adverse effect of the irregular etching is increased and there appears a region which is overly subjected to the etching liquid or etching gas. This tends to give damages to the underground layer(s). Although it is technically possible to remove the peelable layer until it has a thickness of about 20 xcexcm without giving damages to the underground layer(s), the thickness of the peelable layer is preferably 10 xcexcm or less in consideration of the production tact.
In the case where the peelable layer is removed using the plasma etching method in which oxygen is chiefly used, it is preferred that a barrier layer composed of SiOx having a thickness of 0.1 xcexcm or less is disposed between the peelable layer and the transparent conductive layer or an intermediate layer is composed of a material having a resistance against plasma gas and such obtained intermediate layer commonly serves as the barrier layer.
The barrier layer acts as an etching stopper at the time of removal of the peelable layer by etching. In order to clearly understand the terminal point (namely, the timing for ending the etching operation), it is preferred that the peelable layer itself is composed of a colored resin instead of composing the peelable layer from a colorless resin. As a colored resin, aromatic polyimide resins which are originally yellow-colored in the respect of a molecular structure, or those resins which are colored by applying a dye or pigment to a transparent resin can be used. Specific examples of the latter include, as resins, acryl, epoxy and polyimide of a particular structure (which is obtained by adding a silane coupling agent to polyimide synthesized from pyromellitic anhydride and 4,4xe2x80x2-diaminodiphenyl ether), as dyes, C.I. solvent, yellow 63, C.I. solvent blue 25 and acid rhodamine, and as pigments, C.I. pigment blue and C.I. pigment yellow 139. The coloring concentrations of them are preferably 2 to 4 xcexcm in thickness and their minimum penetration factors are about 5 to 60%.
When a layer having a resistance against a plasma gas is formed on the supporting body at the time of forming the transfer body, it can sometimes happen that the color filter layer gets an defect, that cannot be corrected, in hue or other parts at a stage where the formation of the layers has been completed up to the color filter layer. In that case, the transfer body can be reproduced by removing only the color filter layer by a suitable method such as a plasma etching method in which oxygen is chiefly used. By adding a small quantity of gas such as CF4 to the oxygen, the etching can be made quickly compared with the case in which only oxygen is used. However, there is a risk that CF4 attacks SiOx and ITO itself. Therefore, by arranging such that the etching is made using oxygen added with CF4 at an early stage of the etching and the gas to be used is gradually changed to a pure oxygen as the etching process comes closer to the end, there can be obtained an etching which is damageless to the underground layer(s).
Since the removal of the peelable layer and the reproduction of the transfer body are performed by a dry process such as a plasma etching in which oxygen is chiefly used, the method of the present invention has such an advantage that there is no need of discarding exhaust liquid which would otherwise be necessitated as in the conventional method using a solution. Thus, there can be free from the problem for causing an environmental pollution, etc. The barrier layer composed of SiOx have functions serving as an insulating film for the transparent conductive layer placed opposite thereto after panelized and as a protective layer for the transparent conductive layer itself. It further have the functions to improve the gas barrier performance and improve the adhesion between the transparent conductive layer and the color filter layer.